LTE technology has two duplex modes: FDD and TDD. In the FDD mode, a User Equipment (UE) performs uplink transmission and downlink reception at an uplink frequency band and a downlink frequency band respectively, so that the uplink transmission and downlink reception can be performed at the same time. In the TDD mode, the UE performs uplink transmission and downlink reception at different time respectively, so that the uplink transmission and downlink reception cannot be performed at the same time. The spectrum resources of the LTE are mainly of 2,500 to 2,690 MHz, as shown in FIG. 1, the uplink frequency band of LTE FDD is of 2,500 to 2,570 MHz, the downlink frequency band of LTE FDD is of 2,620 to 2,690 MHz, and the frequency band of LTE TDD is of 2,570 to 2,620 MHz.
With the development of radio technology, the FDD&TDD hybrid scheme of the LTE is the mainstream planning scheme in the planning process of a network, so that the network coverage of FDD and TDD may coexist in the same area. If the LTE FDD system and LTE TDD system coexist, the coexistence of adjacent frequency bands will become a primary problem to be solved.
When the LTE FDD system and the LTE TDD system coexist, the adjacent frequency bands between the two systems may be interfered due to out of band emission, spurious emissions and the like as the two systems work at adjacent frequency bands, thereby affecting the network performance. For example, as shown in the scenario in FIG. 2, there are two evolved NodeBs (eNBs) in total, eNB_1 and eNB_2, which cover cell 1 (Cell_1) and cell 2 (Cell_2) in an FDD mode and a TDD mode respectively, wherein Cell_1 and Cell_2 provide a service to UE_1 and UE_2 respectively, the coverage areas of eNB_1 and eNB_2 are somewhat overlapped and both UE_1 and UE_2 are located at the overlapped part of the coverage areas, as in such, if the working frequency bands of eNB_1 and eNB_2 are adjacent, there will be interference between the adjacent frequency bands, specifically, if the TDD working frequency band of eNB_2 is adjacent to the FDD uplink frequency band of eNB_1, the downlink data of eNB_2 may interfere the uplink reception of eNB_1 due to out of band emission and other reasons, namely, the transmission of eNB_2 interferes the reception of eNB_1, and at the same time, the uplink transmission of UE_1 may also interfere the downlink reception of UE_2 at the UE sides; and if the TDD working frequency band of eNB_2 is adjacent to the FDD downlink frequency band of eNB_1, the downlink transmission of eNB_1 may interfere the uplink reception of eNB_2 and the uplink transmission of UE_2 may interfere the downlink reception of UE_1.
To avoid the adjacent-band interference between the TDD system and the FDD system, as shown in FIG. 3, a Guard Band (GB) can be arranged between the FDD and TDD frequency bands but is not available for neither the TDD system nor the FDD system; due to the existence of the GB, there will be a space between the working frequency bands of the LTE FDD system and the LTE TDD system to avoid the adjacent-band interference; whereas, the unavailability of the GB for any system may cause the waste of spectrum resources and is not favourable for the development and popularization and application of TDD technology. Therefore, the interference between frequency bands and the waste of spectrum resources are the primary problems for the coexistence of the FDD system and TDD system of the LTE.
In the LTE, one UE is served by only one Component Carrier (CC) and there is only one component carrier in each cell. The cell corresponding to the component carrier serving the UE is the serving cell of the UE, by which the UE is provided with a series of functions, including secure input, Non Access Stratum (NAS) mobile information, radio link detection, paging and the like. With the gradual advancement of the LTE standard, carrier aggregation technology has become a significant feature of the LTE-Advanced standard. In the carrier aggregation technology, each eNB may be configured with multiple Component Carriers (CC) and the UE may also be configured with and utilize multiple member carriers, including primary component carriers and secondary component carriers. The primary component carrier is the one providing a complete service to the UE in the carrier aggregation, namely, without secondary component carrier, the UE can work normally only by the primary component carrier. The secondary component carrier is introduced to the LTE-Advanced standard to expand the operation bandwidth of the LTE equipment and improve the throughput and cannot provide a complete service to the UE nor exist separately without the primary component carrier. The UE aggregating multiple component carriers may perform transmission and reception on the component carriers. As shown in FIG. 4, UE_1 is configured with three component carriers f1, f2 and f3, and UE_2 is configured with two component carriers f4 and f5, where fn (n is a positive integer), represents carriers of different frequencies. In the carrier frequency band of the LTE, some TDD and FDD carriers may be adjacent to one other in frequency, so these carriers may interfere with one another to cause the LTE system not to work normally and affect the user experience.
For the LTE technology, the implementation of the coexistence of the FDD and TDD systems is confronted with the problems of interference between frequency bands and waste of spectrum resources, which also affect the implementation of carrier aggregation in the LTE-Advanced standard.